(1) Field of the Invention
The present invention relates to a display panel device and a method of manufacturing the same, and in particular to an organic electroluminescence (EL) display panel device.
(2) Description of the Related Art
The organic EL panel devices are luminescent display panel devices using electroluminescence phenomena generated from organic compounds, and have been practically used as small-sized display panel devices, such as those for mobile phones.
Each of the organic EL panel devices includes, on a substrate, an array of organic EL elements capable of controlling a luminescence separately for each pixel.
Typically, each of the organic EL panel devices includes, on a substrate, a controller, a pixel electrode separate for each pixel (for example, anode), an organic functional layer, and a common electrode (for example, cathode). The organic functional layer includes at least an organic EL layer made of an organic compound, and may include at least one of functional layers to be stacked on the organic functional layer. The functional layers include an electron injection layer, an electron transport layer, a hole transport layer, and a hole injection layer.
The organic EL panel device having such a structure produces a luminescence through injection of charges into the organic EL layer through the anode, the cathode, the hole injection layer, and the electron transport layer, and recombination of the injected charges in the organic EL layer.
For example, Japanese Unexamined Patent Application Publications No. 2007-123286 (hereinafter referred to as Patent Reference 1) and No. 2008-72078 (hereinafter referred to as Patent Reference 2) disclose such organic EL display panel devices.
FIG. 8A illustrates a cross section of main portions of an organic EL display device 800 disclosed in Patent Reference 1. The organic EL display device 800 includes a substrate 801, a driving transistor 802, an insulation layer 803, a pixel electrode 804, a bank layer 805, a luminescence material layer 806, and a facing electrode 807.
FIG. 8B illustrates a cross section of main portions of an organic EL display device 900 disclosed in Patent Reference 2. The organic EL display device 900 includes a substrate 901, a thin-film transistor 902, a planarizing layer 903, a first pixel electrode 904, a pixel control layer 905, an organic EL layer 906, and a second pixel electrode 907.
Each of the bank layer 805 of the organic EL display device 800 and the pixel control layer 905 of the organic EL display device 900 has an opening on a favorable area of each of the pixel electrodes, and functions as a bank for defining a luminescent area of each of the pixels. Here, the opening is made of an insulating material.
However, it is known that in a conventional organic EL display panel device, the luminescence function is lost in proximity of a peripheral portion of the opening of a bank, such as that of the bank layer 805 or the pixel control layer 905, and a defect (degradation in pixel) resulting in reduction in a luminescent area occurs.
FIGS. 9A to 9C illustrate the processes of occurrence of such a defect in a conventional organic EL display panel device, using an example of a simplified organic EL element 700.
When the organic EL element 700 is manufactured, a pixel electrode 704 (the pixel electrode 804 and the first pixel electrode 904) is formed by (i) forming a thin layer 704A, such as a metal layer, on an entire surface of a substrate 701 using a thin film formation method, for example, the sputtering method, and (ii) eliminating an unnecessary portion of the thin layer 704A by an etching process using a resist 704M as a mask, thus leaving only a necessary portion of the thin layer 704A, as illustrated in FIG. 9A.
However, when the pixel electrode 704 is formed by a wet etching process, depressed portions each of which is a lateral opening are formed at the end faces of the pixel electrode 704 with the etching solution entering the side of the pixel electrode 704, as illustrated in FIG. 9B. When a bank 705 (the bank layer 805 and the pixel control layer 905) is stacked on the pixel electrode 704 using the thin film formation method, such as a sputtering method and a wet process in the aforementioned state, the depressed portions become closed hollows 708.
The air and moisture accumulated in the hollow 708 enter, in particular, an organic EL layer 706 in the resulting organic EL element 700 as indicated by arrows 709, thus causing degradation in the organic EL layer 706 and in the device characteristics, or deterioration in the life of the device, as illustrated in FIG. 9C.
The present invention has been conceived to solve the problems, and has an object of providing a display panel device with reliability higher than conventional devices, and a method of manufacturing the same.